Our objective is a generalized understanding of the mechanisms by which oxygen supports life. We wish to obtain this understanding in terms of structures of oxygen, oxidases, and substrates, and of mechanisms of oxygen-activating reactions. We propose to work specifically with copper, heme-, and copper-and-heme-containing oxidases. Some progress has been made with the nature of electron donor and oxygen-acceptor interaction with oxidases. However, the nature of catalytic mechanisms involving molecular oxygen itself are virtually unknown in every case. We propose to continue our studies by (1) determining the structures of some copper-, heme-, and copper-and-heme-containing oxidases, particularly their catalytic centers, (2) characterizing reactions taking place between these oxidases, their substrates, and oxygen, (3) determining fates of products when these are metastable and reactive substances and, (4) seeking new techniques for detecting and characterizing functional complexes of oxidases and their substrates with oxygen.